I've wondered about this for quite a while (perhaps fifteen years but forgot about it periodically) and have not been able to find the answer. I can't find the answer on Google, either.
My question is this: why does a spinning flywheel, supported by reasonably sensible bearings* that is allowed to coast down to rest, rock backwards slightly before finally stopping completely? I assume that it doesn't come to rest after the first "rock" or reversal of direction, rather it decays.
*I mention this because I haven't observed it when the bearings of whatever it is are particularly tight or knackered, or there is a lot of parasitic drag, such as when the flywheel has an engine attached. As you'd probably expect.
I have a rubbish video: https://www.youtube.com/watch?v=khXpTaNs9Fw
That's a Technics 1210 with the magnet removed. I removed it for the video to make sure that the rocking at the end of the coasting wasn't caused by the back EMF induced in the motor.
I tried to illustrate that it does it in both directions.
I've been wondering about the zero crossing point, or the point in time between (arbitrarily) clockwise rotation and anticlockwise rotation. In my mind, if the reason it does this is simply that the friction is of a higher magnitude than the inertia (it has to be, otherwise it would not decelerate if it were of an equal magnitude and would accelerate if it were of a lower magnitude) then how can it be of a magnitude significant to overcome the reverse static friction, which is higher than the dynamic friction seen during the deceleration?